1. Field of the Invention
This invention relates to the use of microwave energy to treat multi-component gaseous waste streams. Gaseous waste streams, referred to generally herein as xe2x80x9coff-gasxe2x80x9d, are ubiquitous in all areas of industry and manufacturing. A multitude of industrial processes generates waste off-gas streams which may include a variety of undesirable contaminants, such as volatile organic compounds (VOCs). Thermal processing of solid and liquid waste will frequently generate a separate gaseous waste stream which should desirably be treated prior to release into the environment. At present, gaseous waste streams are frequently treated with filtration systems, chemical cleansing, scrubbers, or chemical conversion to a solid material which is subsequently disposed of as solid waste. However, such methods are expensive and require specialized materials and handling which adds to the disposal and treatment expense. Further, such off-gas treatment methods are not generally suitable or economically feasible for a small volume generator of a contaminated off-gas stream. Unfortunately, small businesses that use or manufacture solvent based VOC materials, such as a dry cleaners, a painting shop, etc., may simply exhaust or discharge the materials into the environment.
Accordingly, there is a need for a low cost, simple to operate waste treatment apparatus and process for low volume gaseous waste generators. Further, there remains a need for further improvement in existing VOC and other gas waste treatment systems over currently available technology. As a result, there remains much room for improvement and variation within the art.
2. Description of Related Art
It is known in the art to use microwaves to treat solid waste. U.S. Pat. No. 5,166,488 to Peppard, incorporated herein by reference, teaches an apparatus which uses microwaves to melt hypodermic syringes. U.S. Pat. No. 4,940,865 provides an apparatus for melting materials using microwaves. However, these microwave treatments result in the generation of gaseous and airborne particulates which require costly filtering and containment systems.
U.S. Pat. No. 5,507,927 to Emery discusses an apparatus for the reduction of organic material through the use of microwave radiation. However, the process taught by Emery results in gaseous products being evolved which are taken to a condenser and condensed to a liquid product.
U.S. Pat. No. 5,270,515 to Long is directed to a microwave plasma process for detoxification of dioxins, furans, and other toxicants. This reference teaches using microwaves to create an ionized plasma state which is controlled through an induced magnetic field. The plasma is used to produce high ionization levels and molecular dissociation without excess heating of the reactants. Such an apparatus and process requires considerable infrastructure and control mechanisms.
U.S. Pat. No. 5,830,328 to Uhm is also directed to using microwave radiation to generate a plasma to decontaminate gaseous emissions. The microwave radiation is conducted through an electric field for generation of a plasma having a high electron temperature. Material is exposed to the plasma for oxidation of the contaminants by atomic oxygen. Uhm requires the specialized equipment and control mechanisms for the creation of a plasma field, and requires the use of plasma torches and other apparatuses so as to maintain a temperature in excess of 3,000 K.
The use of plasma ion fields requires a high investment and operator sophistication which is not economically feasible for many users. Accordingly, there remains room for improvement within the art of microwave processing of gaseous waste.
It is an object of this invention to provide an apparatus and a process to treat off-gas emissions with microwave radiation such that the treated off gas may be discharged into the atmosphere.
It is a further and more particular object of this invention to provide a microwave treatment apparatus useful in the treatment of off-gases.
It is a further and more particular object of this invention to provide an off-gas disposal apparatus and process which uses hybrid microwave heating to treat a wide range of materials contained in off-gas streams.
It is still a further and more particular object of this invention to provide an apparatus and process which can be used to regenerate or purify a stream of an inert process gas in a gas recycling or recovery system.
It is a further object of the present invention to allow for the sterilization of a gaseous stream.
It is an additional object of the present invention to provide an off-gas treatment process in which microwave energy is used to purify an air stream and in which latent heat associated with the purification process is recovered.
It is a further object of the present invention to provide an air purification process and apparatus which can be used to reduce the concentration of odor-causing compounds present in the off-gas system.
It is still a further object of the present invention to provide a microwave purification process and apparatus which allows replacement of catalytic converters from waste streams associated with the combustion of hydrocarbons.
It is still a further object of the invention to develop a small, compact, portable off-gas system of low maintenance, that can be interfaced with various furnaces, ovens or other thermal equipment generating off-gases and to remediate the gases produced during operation.
These and other objects of the invention are accomplished by an apparatus and process that provides for a hybrid microwave off-gas treatment system comprising:
a treatment chamber in communication with a source of microwaves, the treatment chamber having an inlet in communication with an off-gas source, a treatment chamber further defining a susceptor defining a gas permeable matrix in communication with the input region; and
an exhaust outlet in communication with an output region of the treatment chamber, wherein off-gases pass through the inlet into the susceptor region of the treatment chamber whereby the susceptor matrix is maintained at an effective temperature for treating the off-gases, the treated off-gases exiting through an exhaust port.
Such an apparatus enables the process of treating off-gases comprising:
providing a fluid stream having at least one contaminant therein;
directing the fluid stream to a treatment chamber;
radiating the fluid stream in the treatment chamber with microwave energy;
retaining the fluid stream within the treatment chamber until an effective amount of the at least one contaminant is destroyed, thereby providing a treated fluid stream; and
venting the treated fluid stream.
The invention is an improvement over prior methods of using microwave energy to treat gaseous waste. The present invention provides an off-gas treatment process such that a releasable off-gas is produced. Contaminants within the off-gases are combusted to innocuous end products and/or releasable concentrations. The microwave process provides a high temperature environment produced by microwave energy in combination with a susceptor material. The resulting treated off-gas waste is a decontaminated and sterilized off-gas system in which key emissions can be significantly reduced and often may be vented into the atmosphere.